Dolosigranulum pigrum cooperation and competition in human nasal microbiota

Multiple epidemiological studies identify Dolosigranulum pigrum as a candidate beneficial bacterium based on its positive association with health, including negative associations with nasal/nasopharyngeal colonization by the pathogenic species Staphylococcus aureus and Streptococcus pneumoniae. To gain insight into D. pigrums functions, we used a multipronged strategy. We identified in vivo community-level and in vitro phenotypic cooperation by specific nasal Corynebacterium species. D. pigrum inhibited S. aureus growth in vitro. Whereas, D. pigrum plus a nasal Corynebacterium were needed to inhibit S. pneumoniae growth. Moreover, D. pigrum L-lactic-acid production was insufficient for this inhibition. Genomic analysis of 11 strains revealed that D. pigrum has a small genome (average 1.86 Mb) and multiple predicted auxotrophies, which indicate that D. pigrum relies on its human host and cocolonizing bacteria for key nutrients. This shift to genomic and phenotypic experimentation marks a significant advance in understanding D. pigrums role in human nasal microbiota.